Uses of Tetrafluoroethylene

The first [2 + 2] cycloaddition of methylenecyclopropane which has been reported involves the use of tetrafluoroethylene (482) (Table 38, entry 1) [131], an olefin having a high tendency to give cycloadditions in a [2 + 2] fashion, which are considered to occur in a two-step process involving diradical intermediates. In the same article, the author reports unsuccessful attempts to react methylenecyclopropane with maleic anhydride or acrylonitrile [131]. 

EVOLUTION OF ACADEMIC BARRICADES FOR THE USE OF TETRAFLUOROETHYLENE (TEE) IN THE PREPARATION OF FLUOROPOLYMERS... 

Perfluoroepoxid.es were first prepared ia the late 1950s by Du Pont Co. Subsequent work on these compounds has taken place throughout the world and is the subject of a number of reviews (1 5). The main use of these epoxides is as intermediates in the preparation of other fluorinated monomers. Although the polymerisation of the epoxides has been described (6—12), the resulting homopolymers and their derivatives are not significant commercial products. Almost all the work on perfluoroepoxides has been with three compounds tetrafluoroethylene oxide (TFEO), hexafluoropropylene oxide (HFPO), and perfluoroisobutylene oxide (PIBO). Most of this work has dealt with HFPO, the most versatile and by far the most valuable of this class of materials (4). 

The inability to process PTFE by conventional thermoplastics techniques has nevertheless led to an extensive search for a melt-processable polymer but with similar chemical, electrical, non-stick and low-friction properties. This has resulted in several useful materials being marketed, including tetrafluoro-ethylene-hexafluoropropylene copolymer, poly(vinylidene fluoride) (Figure 13.1(d)), and, most promisingly, the copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether. Other fluorine-containing plastics include poly(vinyl fluoride) and polymers and copolymers based on CTFE. 

The earliest materials were copolymers of tetrafluoroethylene and tri-fluoronitrosomethane but they were cross-linked with difficulty and the vulcanisates had little strength. Somewhat better results were obtained using carboxynitrosopolymers of the type... 

A -Halogenated compounds such as iV-chlorotnfluoroacetamide, A -chloro-imidosulfuryl fluonde and N N dichlorotnfluoromethylamine add across C=C bonds to form saturated amides [14] tmidosulfury I fluorides [15] and amines [16], respectively Allylic halogenation also occurs with the use of A-bromo- or A-chIo roperfluoroamides The primary amine A,A-dichlorotrifluororaethylamine selectively affords 11 or 2 1 adducts with either tetrafluoroethylene or chlorotrifluoroethylene [16] (equation 7) The reaction mechanism is believed to involve thermal free radicals, with control achieved principally by reaction temperature The 1 1 adduct is formed even in the presence of a large excess of olefin... 

Materials compatibility. We use scrupulously clean and scratch-free FEP (FEP is the acronym for the copolymer of tetrafluoroethylene and hexafluoropropylene) tubing for handling our mixtures of fluorine and nitrogen at ambient temperature. Corrugated FEP tubing is convenient for making strain-free assemblies. We have found that Monel is excellent for use with dry molten KF-2HF. Mild steel corrodes slowly and stainless steels corrode rapidly. Kel-F polychlorotrifluoroethylene is satisfactory for use with HF and with KF-2HF polypropylene and polymethylpentene are not satisfactory. 

One major use of HF is in the manufacture of fluorinated hydrocarbons. Fluorinated ethylene is used for several specialty polymers. For example, the Teflon coating on nonstick cookware is made from polytetrafluoroethylene (PTFE). This polymer is made from tetrafluoroethylene. 

Mention has already been made of the effectiveness of corona or plasma treatment in increasing the influence of subsequent or concurrent polymer treatment. As examples of polymers used in this way, mention can be made of reactive cationic polysiloxane [294] and polymerisation on the fibre of tetrafluoroethylene or hexafluoropropylene [299]. Water repellency was also improved by the fluorinated polymers. Tetrafluoroethylene gave superior shrink resistance this polymer covered the scale edges of the wool, whereas this did not occur with poly(hexafluoropropylene). 

Fluorinated polymers, especially polytetrafluoroethylene (PTFE) and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene (HFP) and perfluorinated alkyl vinyl ethers (PFAVE) as well as other fluorine-containing polymers are well known as materials with unique inertness. However, fluorinated polymers with functional groups are of much more interest because they combine the merits of pefluorinated materials and functional polymers (the terms functional monomer/ polymer will be used in this chapter to mean monomer/polymer containing functional groups, respectively). Such materials can be used, e.g., as ion exchange membranes for chlorine-alkali and fuel cells, gas separation membranes, solid polymeric superacid catalysts and polymeric reagents for various organic reactions, and chemical sensors. Of course, fully fluorinated materials are exceptionally inert, but at the same time are the most complicated to produce. 

One alternative to the tetrafluoroethylene-based backbones of the previously discussed materials is the use of styrene and particularly its fluorinated derivatives to form PEMs. As extensively reported in the literature, styrenic monomers are widely available and easy to modify, and their polymers are easily synthesized via conventional free radical and other polymerization techniques. 

Fluoroatcohols. A group of fluorine contg alcohols are available commercially having the general formula H(CFa.GF2)nCH20H, in which n = 1 to 5 They include ales contg C3, C, C7, C9 Ctl, Density of Liquids 1.48-1.66, nD 1.318-1.320 (lowest of all known org compds). Derived by. free radical telomerization of tetrafluoroethylene with methanol. Used as solvents and in org synthesis... 

CF2)4 mw 200,04 chemically inert dry gas, bp —6°(760mm) high,electric strength. Can be prepd by dimerization of tetrafluoroethylene at high temp. Used for electric equipment and as aerosol proplnt for foods and pharmaceuticals... 

The copolymer of ethylene and tetrafluoroethylene (ETFE) can be cross-linked by irradiationl Furfher improvemenf is achieved wifh fhe use of prorads, such as TAG or TAIC, in amounfs up fo 10%. 

However, there are many misconceptions concerning uses, applications, and attributes of fluorocarbons. The use of fluorocarbons can be classified into two major categories (1) use of inherent bulk properties, and (2) modification of the surface properties of underlying materials. Once this has been established, the proper choice of fluorocarbon can be evaluated. For the purpose of this discussion, fluorocarbons will be grouped into two categories (1) polymers based on highly fluorinated monomers such as tetrafluoroethylene (TFE), hexafluoropropylene. 

As usual, certain additives can be added to the composition. Among others, the use of an anti-drip agent has been proposed, namely poly(tetrafluoroethylene) (PTFE)). The anti-drip agent may be encapsulated by a rigid copolymer, for example, SAN, which is known as teflon encapsualed in SAN (TSAN) (29). 

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